The identification of members the G-protein coupled, seven-transmembrane domain, receptor (GPCR) family as coreceptors for cellular entry of human immunodeficiency virus (HIV) was a landmark finding that has begun to define at a mechanistic level many of the pathogenetic observations and tropism differences that have been described in association with HIV infection. The CNS contains many GPCRs, including most of the major chemokine receptors that have been implicated in HIV infection as well others that can function as HIV coreceptors in fusion and other assays, but whose function in actual infections is not yet known. Significantly, CCR3 may have a specific role in tropism of viruses for microglial cells (He at al., 1997), and hippocampal neurons express CXCR4 and CCR3. The principal hypotheses in this proposal are that the expression of chemokine receptors and other GPCRs within the CNS plays a major role in the development and pathogenesis of HIV dementia by (1) potentially defining the HIV strains that can establish a chronic CNS infection, (2) serving as a potential route for neuronal pathology mediated by HIV, perhaps by mediating binding by gp120, and, (3) possibly serving as primary receptors for HIV infection of CD4-negative cells. Concomitantly, chemokine expression in the CNS may influence HIV strain variability and neuronal function, since chemokine receptors have been detected in neurons. These hypotheses will be tested with three major specific aims: (1) We will determine which chemokine receptors are used by isolates in the CNS, primarily using envelopes cloned directly from infected brains and a combination of assays including cell-to-cell fusion, preparation of pseudotype viruses, and HIV infection of cells transiently transfected with individual chemokine receptors (2) We will determine which HIV coreceptors are expressed in microglia, neurons, and other cells of the CNS using immunohistochemistry, in-situ hybridization, and reverse transcriptase-PCR amplification (RT/PCR) in brain and in cultured CNS cells. We will also determine whether there are differences in the level of expression between brains obtained from HIV-infected individuals with/without HIV encephalitis and individuals with other inflammatory neurological diseases. (3) We will use ELISA and RT-PCR to determine which of the known chemokines are expressed by HIV infected microglia, by other CNS cells, and in HIV infected histological specimens. The results of these studies will further our understanding of the pathophysiology of HIV dementia.